Lubricated Hirth serration coupling

ABSTRACT

Apparatus and methods for coupling components of dissimilar materials via a Hirth serration coupling, wherein an interfacial layer at a Hirth teeth interface allows radial sliding motion of a first set of Hirth teeth relative to a second set of Hirth teeth. The interfacial layer may be a solid lubricant coating, or a compliant multi-layered metal sheet.

BACKGROUND OF THE INVENTION

The present invention relates to Hirth serration coupling of dissimilar materials, and to methods for coupling components comprising dissimilar materials via a lubricated Hirth teeth interface.

Coupling of components comprising dissimilar materials using typical form-locking teeth, such as curvic couplings, do not allow relative radial movement of the coupled components. Consequently, using curvic couplings to couple two dissimilar components, such as a ceramic rotor to a metal rotor in a gas turbine (hot section) environment, would result in unacceptably high contact stresses at the ceramic/metal teeth interface due to differential thermal expansion of the two components. Such contact stresses could lead to rotor eccentricity, bowing, poor running performance, and possible component failure.

Metal to metal Hirth serration couplings are known in the art. In Hirth serration couplings, the geometry of planar Hirth teeth surfaces would theoretically allow coupled dissimilar components to move radially relative to one another during transient operation. In practice, however, radial movement of coupled components relative to one another following differential thermal expansion may be prevented, for example, due to friction at the interface of the Hirth teeth, which may result in tensile stress peaks at the Hirth teeth interface and possible component failure. Accordingly, coupling of dissimilar materials exposed to thermal cycling, such as a ceramic rotor of a hot section gas turbine engine coupled to a metal rotor, has not been feasible heretofore.

U.S. Pat. No. 6,672,786 to Schenk discloses a solid lubricant and a compliant sleeve for coupling a ceramic stub shaft to an annular shrink fitter via an interference fit. U.S. Pat. No. 6,132,175 to Cai et al. discloses a compliant sleeve for mounting a lobed root portion of a ceramic airfoil to a mating slot of a metal disk.

As can be seen, there is a need for apparatus and methods that will allow the coupling of dissimilar materials via a Hirth serration coupling for operation during thermal cycling.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided an apparatus comprising a first component; a second component coupled to the first component via a Hirth serration coupling, the Hirth serration coupling defining a Hirth teeth interface between the first component and the second component; and an interfacial layer disposed at the Hirth teeth interface, wherein the interfacial layer is adapted for allowing radial sliding motion of the second component relative to the first component at the Hirth teeth interface.

According to another aspect of the present invention, there is provided an apparatus comprising a ceramic component, and a metal component rotatably coupled to the ceramic component via a Hirth serration coupling.

According to a further aspect of the present invention, an apparatus may include a first component comprising a ceramic rotor and having a first set of Hirth teeth; a second component comprising a metal and having a second set of Hirth teeth for engaging the first set of Hirth teeth to provide a Hirth serration coupling of the first component to the second component, the Hirth serration coupling defining a Hirth teeth interface between the first set of Hirth teeth and the second set of Hirth teeth, wherein a CTE mismatch exists between the first component and the second component; and an interfacial layer disposed at the Hirth teeth interface. The interfacial layer may be adapted for allowing radial sliding motion of the second component relative to the first component at the Hirth teeth interface, and the interfacial layer may comprise a solid lubricant coating, or a compliant metal layer.

According to still a further aspect of the present invention, there is provided a gas turbine engine comprising a ceramic rotor having a first set of Hirth teeth; a metal coupler axially aligned with, and disposed adjacent to, the ceramic rotor, the metal coupler having a second set of Hirth teeth and the metal coupler coupled to the ceramic rotor via a Hirth serration coupling to define a Hirth teeth interface; and an interfacial layer disposed at the Hirth teeth interface, wherein the interfacial layer comprises a solid lubricant coating adhered to the second set of Hirth teeth, or a multi-layered pre-formed metal sheet.

According to still another aspect of the present invention, a method for coupling components may include steps of: providing a first component having a first set of Hirth teeth; providing a second component having a second set of Hirth teeth; coupling the first component to the second component via a Hirth serration coupling to define a Hirth teeth interface between the first set of Hirth teeth and the second set of Hirth teeth, wherein an interfacial layer is disposed at the Hirth teeth interface; applying a rotational force to the first component; and via the Hirth serration coupling, transmitting torque from the first component to the second component.

According to yet another aspect of the present invention, a method for coupling components comprises forming a compliant metal layer, providing a first component having a first set of Hirth teeth, providing a second component having a second set of Hirth teeth, and coupling the first component to the second component via a Hirth serration coupling such that the compliant metal layer is disposed at a Hirth teeth interface between the first set of Hirth teeth and the second set of Hirth teeth.

According to yet a further aspect of the present invention, a method for coupling components comprises providing a first component having a first set of Hirth teeth; providing a second component having a second set of Hirth teeth; depositing a solid lubricant coating on the second set of Hirth teeth; coupling the first component to the second component via a Hirth serration coupling to define a Hirth teeth interface between the first set of Hirth teeth and the second set of Hirth teeth, wherein the solid lubricant coating is disposed at the Hirth teeth interface; applying a rotational force to the first component; and via the Hirth serration coupling, transmitting torque from the first component to the second component.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically representing a gas turbine engine, according to one aspect of the invention;

FIG. 2A schematically represents apparatus having a first component coupled to a second component via a Hirth serration coupling, according to one embodiment of the invention;

FIG. 2B schematically represents apparatus having a first component coupled to a second component and a third component via a Hirth serration coupling, according to the invention;

FIG. 3A is a plan view of a first set of Hirth teeth engaged by a second set of Hirth teeth to define a Hirth teeth interface therebetween, according to the invention;

FIG. 3B is a perspective view of a portion of a set of Hirth teeth, according to another aspect of the invention;

FIG. 4A is a plan view of a grinding wheel in relation to a first component having a first set of Hirth teeth cut therein, according to another aspect of the invention;

FIG. 4B is a side view of the grinding wheel in relation to the first component indicating a direction of cutting the first set of Hirth teeth relative to the location of the first component, according to the invention;

FIG. 5A is a plan view of a grinding wheel in relation to a second component having a second set of Hirth teeth cut therein, according to the invention;

FIG. 5B is a side view of the grinding wheel in relation to the second component indicating a direction of cutting the second set of Hirth teeth relative to the location of the first component, according to the invention;

FIG. 6A is a side view of a Hirth tooth of a first component;

FIG. 6B is a sectional view taken along the line 6B-6B of FIG. 6A, according to another embodiment of the invention;

FIG. 6C is a side view of a Hirth tooth of a second component;

FIG. 6D is a sectional view taken along the line 6D-6D of FIG. 6C, according to another aspect of the invention;

FIG. 7 is a perspective view of an apparatus comprising a first component coupled to a second component via a Hirth serration coupling, according to another embodiment of the invention;

FIG. 8 schematically represents a solid lubricant coating disposed on a Hirth tooth surface of a metal component, according to another embodiment of the invention;

FIG. 9 schematically represents a multi-layered compliant metal sheet disposed at a Hirth teeth interface between a first component and a second component, according to another embodiment of the invention;

FIG. 10 schematically represents a series of steps involved in a method for coupling components, according to another embodiment of the invention; and

FIGS. 11A and 11B each schematically represents a series of steps involved in a method for coupling components, according to two different embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Broadly, the present invention provides apparatus and methods for coupling components comprising dissimilar materials via Hirth serration couplings. The present invention may be used to axially couple rotary components, wherein a coefficient of thermal expansion (CTE) mismatch may exist between the coupled components, and wherein the components may be exposed to thermal cycling. As a non-limiting example, the present invention may be used in turbomachinery to couple a ceramic rotor to a metal rotor, for transmitting torque between the ceramic rotor and the metal rotor. In a more specific example, the present invention may be used to couple a ceramic rotor to a metal rotor in a turbine (hot) section of a gas turbine engine. It is to be understood however, that the present invention is not limited to turbomachinery.

In contrast to the prior art, apparatus of the invention may comprise a first component coupled to a second component via a Hirth serration coupling to define a Hirth teeth interface therebetween, wherein an interfacial layer is disposed at the Hirth teeth interface, thereby allowing radial sliding motion of the second component relative to the first component at the Hirth teeth interface. Such radial sliding motion of the second component relative to the first component at the Hirth teeth interface allows components of dissimilar materials, and having a CTE mismatch therebetween, to be coupled via Hirth serration couplings. As an example, apparatus of the present invention which may be exposed to thermal cycling may comprise a ceramic component, and a metal component rotatably coupled to the ceramic component via a Hirth serration coupling, wherein an interfacial layer may be disposed at the Hirth teeth interface to allow radial sliding motion of the metal component relative to the ceramic component. In the prior art, CTE mismatch between metal and ceramic components has prevented coupling of metal components to ceramic components via Hirth serration couplings.

FIG. 1 is a sectional view schematically representing a gas turbine engine 10, which may include an air intake 12, a compressor or compressor section 14, a combustor 16, a turbine or turbine section 18, and a jet nozzle 20. Compressor 14 may compress air from air intake 12, and fuel may be burnt in combustor 16 to produce a high-temperature combustion gas for driving turbine 18. Compressor 14 may be driven by turbine 18 via a shaft 26. Each of compressor 14 and turbine 18 may comprise a plurality of coupled rotatable banks 24 of rotor blades. One or more annular non-rotatable banks 22 of stator vanes may be disposed between the rotatable banks 24 of rotor blades. Herein, the term “blade” may be used generically to refer to the airfoil portion of a rotor or a stator. Each of rotatable banks 24 of rotor blades may comprise a ceramic or a metal. Metal rotors may have separate blades comprising an airfoil portion and a lobed root portion for attachment of the blade to the rotor. Ceramic rotors may comprise a single component having integral blades.

The general arrangement of gas turbine engine 10, and the alternating arrangement of stator vanes and rotor blades are known in the art. In the present invention, dissimilar materials, for example, a ceramic rotor and a metal rotor, of either compressor 14 or turbine 18, and having a CTE mismatch therebetween, may be coupled via a Hirth serration coupling to define a Hirth teeth interface, wherein an interfacial layer may be disposed at the Hirth teeth interface (see, for example, FIG. 2A). Herein, the term “rotor” may be used generically to refer to a rotatable component for turbomachinery or non-turbomachinery applications.

FIG. 2A schematically represents apparatus 30 having a first component 40 coupled to a second component 50 via a Hirth serration coupling to define a Hirth teeth interface 60, according to one embodiment of the present invention. An interfacial layer 70 may be disposed at Hirth teeth interface 60. Each of first component 40 and second component 50 may comprise a rotor or rotary component. First component 40 and second component 50 may be mounted on a shaft (not shown in FIG. 2A).

First component 40 and second component 50 may comprise dissimilar materials. First component 40 may have a first coefficient of thermal expansion (CTE), while second component 50 may have a second CTE, such that a CTE mismatch exists between first component 40 and second component 50. As a non-limiting example, first component 40 may comprise a ceramic, which may have a CTE in the range of 3×10⁻⁶° C.⁻¹ to 5×10⁻⁶° C.⁻¹, and second component 50 may comprise a metal, which may have a CTE two to three times (2×-3×) higher than that of first component 40.

Interfacial layer 70 may be adapted to allow radial sliding motion, of second component 50 relative to first component 40 at Hirth teeth interface 60, resulting from differential thermal expansion of first component 40 with respect to second component 50. Such differential thermal expansion may occur during transient operating conditions, such as start-up and shut-down. Interfacial layer 70 may comprise, for example, a solid lubricant coating (see, for example, FIG. 8), or a compliant metal layer (see, for example, FIG. 9). In the absence of interfacial layer 70 at Hirth teeth interface 60, thermally-induced differential expansion of first component 40 relative to second component 50 may be inhibited, possibly resulting in premature component failure.

FIG. 2B schematically represents apparatus 30′ having a first component 40 coupled to a second component 50 via a Hirth serration coupling, generally as described hereinabove with respect to FIG. 2A. Apparatus 30′ may further include a third component 40′ coupled to second component 50 via a Hirth serration coupling, to define a Hirth teeth interface 60′, according to an embodiment of the present invention. An interfacial layer 70 may be disposed at each Hirth teeth interface 60, 60′. Second component 50 and third component 40′ may be dissimilar materials having a CTE mismatch therebetween. As a non-limiting example, each of first and third components 40, 40′ may comprise a ceramic rotor, while second component 50 may comprise a metal coupler or spacer. In some embodiments, second component 50 may serve to axially space first component 40 from third component 40′ to accommodate a bank of stator vanes therebetween. First component 40 and third component 40′ may each comprise a ceramic such as silicon carbide or silicon nitride. Second component 50 may comprise a metal such as steel, a titanium alloy, or a Ni- or Co-based superalloy.

Apparatus 30, 30′ may find applications in a turbine or compressor of a gas turbine engine. However, it is to be understood that the invention is by no means limited to turbomachinery. Instead, the present invention may be generally applicable to coupling of dissimilar materials via Hirth serration couplings.

FIG. 3A is a plan view of a first set of Hirth teeth 42 engaged by a second set of Hirth teeth 52 to define a Hirth teeth interface 60 therebetween, according to an aspect of the present invention. First set of Hirth teeth 42 may comprise a first material having a first CTE, while second set of Hirth teeth 52 may comprise a second material having a second CTE, wherein a CTE mismatch may exist between first set of Hirth teeth 42 and second set of Hirth teeth 52. First set of Hirth teeth 42 may be formed or cut on a first component 40, and second set of Hirth teeth 52 may be formed or cut on a second component 50, whereby first and second component 40, 50 may be coupled by a Hirth serration coupling (see, for example, FIGS. 2A-B). First component 40 and second component 50 may comprise a first rotor and a second rotor, respectively. An interfacial layer 70 (omitted from FIG. 3A for the sake of clarity) may be disposed at Hirth teeth interface 60. Interfacial layer 70 may comprise, for example, a solid lubricant coating (FIG. 8) or a compliant metal layer (FIG. 9). A gap G may exist between adjacent tooth outer surfaces 82 (FIG. 3B).

FIG. 3B is a perspective view of a portion of a set of Hirth teeth 42′ which may comprise a plurality of teeth 80. Each tooth 80 may include a tooth outer surface 82 disposed between a tooth first side 84 and a tooth second side 86, and an inter-tooth surface 88. Tooth first side 84, tooth second side 86, and inter-tooth surface 88 may jointly define an inter-tooth void 87. Each of tooth outer surface 82, tooth first side 84, tooth second side 86, and inter-tooth surface 88 may comprise a planar surface.

In some embodiments, an interfacial layer 70 (see, for example, FIG. 2A) which may comprise a solid lubricant coating 91 (see, for example, FIG. 8), may be disposed on the tooth outer surface 82, tooth first side 84, tooth second side 86, and inter-tooth surface 88 of each tooth 80/80′. Alternatively, solid lubricant coating 91 may be restricted to tooth first side 84 and tooth second side 86. Solid lubricant coating 91 is omitted from FIG. 3B for the sake of clarity.

FIG. 4A is a plan view of a grinding wheel GW in relation to a first component 40, for cutting a first set of Hirth teeth 42 in first component 40, according to one aspect of the invention. Each inter-tooth void 87 (FIG. 3B) of first set of Hirth teeth 42 may be cut radially with respect to the longitudinal axis (indicated by line X1, FIG. 4B) of first component 40, thereby allowing radial motion of first component 40 when coupled to another component comprising a dissimilar material (e.g., second component 50, FIGS. 2A-B). As a non-limiting example, first component 40 may be a ceramic rotor for a turbine section 18 of a gas turbine engine 10.

FIG. 4B is a side view of the grinding wheel GW in relation to first component 40, in which arrow A1 indicates a direction of cutting of the first set of Hirth teeth 42, i.e., in a direction away from first component 40 when the grinding wheel GW is moved centripetally (i.e., towards the axis of first component 40). Arrow A1 may be at an angle E with respect to axis X1 of first component 40 (FIG. 6B). As a result, first inter-tooth surface 88 may be disposed at angle θ with respect to the axis X1 of first component 40 (see, for example, FIGS. 6A-B). Alternatively, if the grinding wheel GW is moved centrifugally (i.e., towards the circumference of first component 40), a direction of cutting of the first set of Hirth teeth 42 may be towards first component 40, as indicated by arrow A1′. Of course, the angle θ of first inter-tooth surface 88 is the same regardless of whether grinding wheel GW may be moved centripetally or centrifugally. First component 40 may comprise a material having a first CTE which may be less than a second CTE of a material comprising a second component 50 (see FIGS. 5A-B).

FIG. 5A is a plan view of a grinding wheel in relation to a second component 50 having a second set of Hirth teeth 52 cut therein, according to another aspect of the invention. Each inter-tooth void 87 of second set of Hirth teeth 52 may be cut radially with respect to the longitudinal axis (indicated by line X2, FIG. 5B) of second component 50, thereby allowing radial motion due to differential expansion or contraction of second component 50 with respect to first component 40 (see, e.g., FIGS. 2A-B). As a non-limiting example, second component 50 may be a metal rotor for axial coupling to one or more ceramic rotors via Hirth serration couplings. Second component 50 may act as a spacer for coupling, and axially spacing, a pair of ceramic rotors.

FIG. 5B is a side view of the grinding wheel GW in relation to second component 50, in which arrow A2 indicates a direction of cutting of the second set of Hirth teeth 52, i.e., in a direction away from second component 50 when the grinding wheel GW is moved centrifugally (i.e., towards the circumference of second component 50). Alternatively, if the grinding wheel GW is moved centripetally (i.e., towards the axis, X2, of second component 50), a direction of cutting of the second set of Hirth teeth 52 may be towards second component 50, as indicated by arrow A2′. As a result, second inter-tooth surface 88′ may be disposed at angle θ with respect to the axis X2 of second component 50, i.e., the same angle as that at which first inter-tooth surface 88 may be disposed with respect to the axis X1 of first component 40 (see, for example, FIGS. 6A-D). Second component 50 may comprise a material having a second CTE which may be greater than a first CTE of a material comprising first component 40.

FIG. 6A is a side view of a Hirth tooth 80 of first component 40, and FIG. 6B is a sectional view taken along the line 6B-6B of FIG. 6A, according to the invention. Tooth 80 may include tooth outer surface 82 (see, for example, FIG. 3B). First inter-tooth surface 88 and tooth outer surface 82 of first component 40 may each be disposed at an angle θ to the axis X1 of first component 40, such that first inter-tooth surface 88 may be angled away from first component 40 in a direction towards axis X1.

FIG. 6C is a side view of a Hirth tooth 80′ of second component 50, and FIG. 6D is a sectional view taken along the line 6D-6D of FIG. 6C, according to another aspect of the invention. Tooth 80 may include tooth outer surface 82′. Second inter-tooth surface 88′ and tooth outer surface 82′ of second component 50 may each be disposed at angle E to the axis X2 of second component 50, such that second inter-tooth surface 88′ may be angled towards second component 50 in a direction towards axis X2. The angle E may be an acute angle, the value of which may typically be in the range of from about 70 to 87°, usually from about 75 to 86°, and often from about 80 to 85°.

FIG. 7 is a perspective view of an apparatus 30″ comprising a first component 40 coupled to a second component 50 via a Hirth serration coupling to define a Hirth teeth interface 60, according to an embodiment of the invention. First component 40 may be a first rotor and second component 50 may be a second rotor axially aligned with first component 40. First component 40 may comprise a ceramic rotor having a plurality of integral blades 44. Each blade 44 may comprise an airfoil. Second component 50 may comprise a metal rotor. As an example, second component 50 may comprise steel, a titanium alloy, or a superalloy, such as a Ni- or Co-based superalloy. Second component 50 may function as a spacer, and may be used to couple a first ceramic rotor to a second ceramic rotor. An interfacial layer 70 (see, for example, FIGS. 2A-B, and FIGS. 8-9) may be disposed at Hirth teeth interface 60. Interfacial layer 70 is omitted from FIG. 7 for the sake of clarity.

FIG. 8 schematically represents an interfacial layer 70 a disposed on a tooth surface 80′a of a Hirth tooth 80′, according to one embodiment of the invention. Hirth tooth 80′ may be cut in a metal rotor, such as second component 50. In some embodiments, interfacial layer 70 a may comprise a bond coat 90 disposed on tooth surface 80′a of Hirth tooth 80′, and a solid lubricant coating 91 disposed on bond coat 90. Bond coat 90 may comprise, as an example, a layer of chromium (Cr) or a Cr alloy. Bond coat 90 and solid lubricant coating 91 may each be deposited by a deposition process such as sputter coating. Solid lubricant coating 91 may comprise a noble metal, a metal oxide, a molten glass, or mixtures thereof. For example, solid lubricant coating 91 may comprise a material such as gold, silver, platinum, cobalt oxide, boron nitride, boron oxide, or mixtures thereof. Solid lubricant layers are disclosed in commonly assigned U.S. Pat. No. 6,672,786, the disclosure of which is incorporated by reference herein in its entirety.

FIG. 9 schematically represents an interfacial layer 70 b disposed at a Hirth teeth interface 60 (see, e.g., FIGS. 2A-B) between a first Hirth tooth 80 of a first component 40 and a second Hirth tooth 80′ of a second component 50, according to another embodiment of the invention. Interfacial layer 70 b may comprise a compliant metal layer.

In some embodiments, interfacial layer 70 b may comprise a multi-layered pre-formed metal sheet, including an inner substrate layer 92, a first lubricant layer 94 disposed on a first surface 92 a of substrate layer 92, a soft metal layer 96 disposed on a second surface 92 b of substrate layer 92, and a second lubricant layer 98 disposed on soft metal layer 96. Interfacial layer 70 b may have an overall thickness in the range of from about 100 to 325 microns.

Interfacial layer 70 b may be oriented at Hirth teeth interface 60 such that first lubricant layer 94 lies adjacent to second Hirth tooth 80′, and second lubricant layer 98 lies adjacent to first Hirth tooth 80, wherein first Hirth tooth 80 may comprise a ceramic, and second Hirth tooth 80′ may comprise a metal.

Substrate layer 92 may comprise a superalloy, such as a solid solution strengthened Ni- or Co-based superalloy. Substrate layer 92 may have a thickness typically in the range of from about 75 to 250 microns, usually from about 100 to 200 microns, and often from about 100 to 150 microns.

Soft metal layer 96 may comprise a relatively soft, low strength material, having a yield strength less than that of substrate layer 92. For example, soft metal layer 96 may comprise a metal such as nickel, cobalt, platinum, rhodium, or mixtures thereof, or a metal oxide, such as nickel oxide, cobalt oxide, or mixtures thereof, including mixtures of one or more metals with one or more oxides. Soft metal layer 96 may have a thickness typically in the range of from about 25 to 75 microns, usually from about 35 to 65 microns, and often from about 40 to 60 microns.

First lubricant layer 94 may comprise a mixture of hexagonal boron nitride and boron oxides, or a metal oxide such as a cobalt oxide. Second lubricant layer 98 may comprise a soft metal such as gold, or silver, or one or more molten glasses such as borosilicate glasses, and mixtures of hexagonal boron nitride and boron oxides, or mixtures or combinations thereof. Second lubricant layer 98 may have a thickness typically in the range of from about 1 to 5 microns, and usually from about 2 to 4 microns. A multi-layered compliant sleeve was disclosed in commonly assigned U.S. Pat. No. 6,672,786, and commonly assigned U.S. Pat. No. 6,132,175 to Cai et al., the disclosure of each of which is incorporated by reference herein in its entirety.

FIG. 10 schematically represents a series of steps involved in a method 100 for coupling components via a Hirth serration coupling, according to another embodiment of the invention, wherein step 101 may involve providing a first component having a first set of Hirth teeth. Step 102 may involve providing a second component having a second set of Hirth teeth. In some embodiments, the first component may comprise a ceramic, and the second component may comprise a metal. The first and second sets of Hirth teeth may be cut, for example, as described with reference to FIGS. 4A-6D.

Step 103 may involve coupling the first and second components via a Hirth serration coupling, by engaging the first set of Hirth teeth with the second set of Hirth teeth, to define a Hirth teeth interface between the first set of Hirth teeth and the second set of Hirth teeth. An axial clamping force may be applied between the coupled first and second components in order to transmit torque therebetween. In step 103, the first component may be coupled to the second component such that an interfacial layer may be disposed at the Hirth teeth interface. The first and second components may comprise dissimilar materials, which may have different CTE values such that a CTE mismatch may exist between the first and second components. The first component may comprise a material having a first CTE, and the second component may comprise a material having a second CTE, wherein the first CTE may be less than the second CTE. The interfacial layer may be adapted for allowing radial sliding motion of the second set of Hirth teeth relative to the first set of Hirth teeth at the Hirth teeth interface. Such radial sliding motion allows for differential thermal expansion of the first and second components, for example, during transient operating conditions, and thus permits Hirth serration coupling of dissimilar materials having a CTE mismatch.

The interfacial layer may be in the form of a solid lubricant coating disposed on at least one surface of the first or second sets of Hirth teeth. Typically, the solid lubricant coating may be deposited on Hirth teeth of a metal component. The solid lubricant coating may comprise a material such as a noble metal, a metal oxide, a molten glass, or mixtures thereof. The solid lubricant coating may be disposed on a bond coat comprising Cr or a Cr alloy, for example, as described with reference to FIG. 8.

In alternative embodiments, the interfacial layer may comprise a compliant metal layer, which may be in the form of a multi-layered pre-formed metal sheet. Such a pre-formed metal sheet may be disposed at the Hirth teeth interface between the first and second sets of Hirth teeth during coupling of the first and second components. The compliant metal layer may include components and compositions as described hereinabove, for example, with reference to FIG. 9.

Step 104 may involve applying a rotational force or torque to the first component. The first component may be mounted on a shaft, and the rotational force may be applied to the first component via the shaft. Step 105 may involve transmitting torque from the first component to the second component via the Hirth serration coupling.

FIG. 11A schematically represents a series of steps involved in a method 110 for coupling components, according to another embodiment of the invention, wherein step 111 may involve forming a compliant metal layer. The compliant metal layer may be a multilayered, pre-formed metal sheet. The compliant pre-formed metal sheet may be formed by providing an inner substrate layer having a first surface and a second surface, forming a first lubricant layer on the first surface of the substrate layer, forming a soft metal layer on the second surface of the substrate layer, and forming a second lubricant layer on the soft metal layer. The first lubricant layer may define a metal-contacting side, and the second lubricant layer may define a ceramic-contacting side.

The soft metal layer may be applied to the substrate layer by various deposition processes, including: electroplating, sputtering, physical vapor deposition, or chemical vapor deposition, and the like. Thereafter, a vacuum heat treatment may be used to diffusion bond the soft metal layer to the substrate layer. During this heat treatment, alloying elements in the substrate layer (e.g., Ni, Co, Cr, W) may diffuse into the soft metal layer.

In some embodiments, the substrate layer may comprise a superalloy substrate having a first surface and a second surface. The second surface of the superalloy substrate may be plated with a layer of nickel followed by a layer of platinum. The superalloy substrate may then be oxidized to form a nickel oxide scale on the second surface, and a cobalt oxide scale on the first surface. A lubricious coating of boron nitride may then be applied on the cobalt oxide scale, and a shear-stress limiting gold coating may be applied over the nickel oxide scale.

Step 112 may involve providing first and second components to be coupled. The first component may comprise a first material and may include a first set of Hirth teeth, and the second component may comprise a second material and may include a second set of Hirth teeth, wherein a CTE mismatch exists between the first and second materials. As an example, the first component may comprise a ceramic rotor, and the second component may comprise a metal rotor.

Step 113 may involve coupling the first and second components via a Hirth serration coupling to define a Hirth teeth interface between the first and second sets of Hirth teeth, wherein the compliant metal layer may be disposed at the Hirth teeth interface. An axial clamping force may be applied between the coupled first and second components in order to transmit torque therebetween. Thereafter, a rotational force may be applied to the first component (in step 114), and torque may be transmitted from the first component to the second component via the Hirth serration coupling (in step 115), essentially as described hereinabove, e.g., with reference to method 100 (FIG. 10). Due to differential thermal expansion of the first and second components, the compliant metal layer may allow radial sliding motion of the first and second sets of Hirth teeth at the Hirth teeth interface.

FIG. 11B schematically represents a series of steps involved in a method 120 for coupling components, according to another embodiment of the invention, wherein step 121 may involve providing a first component having a first set of Hirth teeth. Step 122 may involve providing a second component having a second set of Hirth teeth. The first and second components may comprise dissimilar materials, such that a CTE mismatch may exist therebetween, for example, as described hereinabove with reference to method 110 (FIG. 11A). As an example, the first set of Hirth teeth may comprise a ceramic, and the second set of Hirth teeth may comprise a metal.

Step 123 may involve depositing a solid lubricant coating on the surface of the second set of Hirth teeth. The solid lubricant coating may comprise a noble metal, such as gold (Au). The solid lubricant may be deposited on a bond coat by sputter coating. As an example, the bond coat may comprise chromium (Cr) or a Cr alloy. The solid lubricant coating may have a thickness typically in the range of from about 2 to 3 microns.

Step 124 may involve coupling the first and second components via a Hirth serration coupling to define a Hirth teeth interface between the first and second sets of Hirth teeth, wherein the solid lubricant coating may be disposed on the second set of Hirth teeth at the Hirth teeth interface. An axial clamping force may be applied between the coupled first and second components in order to transmit torque therebetween. Thereafter, a rotational force may be applied to the first component (in step 125), and torque may be transmitted from the first component to the second component via the Hirth serration coupling (in step 126), essentially as described hereinabove, e.g., with reference to method 100 (FIG. 10), wherein the solid lubricant coating may allow radial sliding motion at the Hirth teeth interface during differential thermal expansion or contraction of the first component relative to the second component.

EXAMPLE

Forming a Solid Lubricant Coating on the Surface of Hirth Teeth

After cleaning the component to be coated (e.g., using isopropanol and deionized water), the component was masked to expose only the teeth surfaces to be coated. The masked component was sputter etched for a period of at least 10 minutes (e.g., using a Technics 4404 RF sputtering machine, pumped down to 10⁻⁶ Torr) preparatory to sputter coating a bond coat of Cr or a Cr alloy to a thickness of about 2,000 Å (0.2 microns). After switching targets, the system was pumped down for sputter etching as described above. Thereafter, using established gas flows, a solid lubricant coating of Au was sputter coated on the bond coat to a thickness of about 2.5 microns (25,000 Å).

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims. 

1. An apparatus, comprising: a first component; a second component coupled to said first component via a Hirth serration coupling, said Hirth serration coupling defining a Hirth teeth interface between said first component and said second component; and an interfacial layer disposed at said Hirth teeth interface, wherein said interfacial layer is adapted for allowing radial sliding motion of said second component relative to said first component at said Hirth teeth interface.
 2. The apparatus of claim 1, wherein: a first coefficient of thermal expansion (CTE) of said first component is less than a second coefficient of thermal expansion (CTE) of said second component.
 3. The apparatus of claim 2, wherein: said first component is a ceramic rotor, and said second component comprises a metal rotor.
 4. The apparatus of claim 1, wherein: said first component is a first rotor, and said second component is a second rotor axially aligned with said first rotor.
 5. The apparatus of claim 1, wherein said interfacial layer is selected from the group consisting of a solid lubricant coating and a compliant metal layer.
 6. The apparatus of claim 5, wherein: said compliant metal layer comprises a pre-formed metal sheet, said pre-formed metal sheet comprises a plurality of layers including: an inner substrate layer, a first lubricant layer disposed on a first surface of said substrate layer, a soft metal layer disposed on a second surface of said substrate layer, and a second lubricant layer disposed on said soft metal layer.
 7. The apparatus of claim 6, wherein: said substrate layer comprises a superalloy, and said first lubricant layer comprises a metal oxide.
 8. The apparatus of claim 6, wherein said first lubricant layer comprises cobalt oxide.
 9. The apparatus of claim 6, wherein said soft metal layer is selected from the group consisting of nickel, cobalt, platinum, rhodium, nickel oxide, cobalt oxide, and mixtures thereof.
 10. The apparatus of claim 6, wherein said second lubricant layer is selected from the group consisting of gold, silver, platinum, boron nitride, boron oxide, and mixtures thereof.
 11. The apparatus of claim 6, wherein said first lubricant layer comprises boron nitride, and said second lubricant layer comprises gold or silver.
 12. The apparatus of claim 6, wherein: said first component comprises a ceramic, said first component includes a first set of Hirth teeth, and said second lubricant layer lies adjacent to said first set of Hirth teeth.
 13. The apparatus of claim 6, wherein said pre-formed metal sheet has a thickness in the range of from about 100 to 325 microns.
 14. The apparatus of claim 1, wherein: said interfacial layer comprises a solid lubricant coating, said second component comprises a metal, said second component includes a second set of Hirth teeth, said solid lubricant coating is disposed on said second set of Hirth teeth, and said solid lubricant coating is adhered to said second component.
 15. The apparatus of claim 14, wherein said solid lubricant coating is deposited on said second component by a sputtering process to a thickness of from about 2 to 3 microns.
 16. The apparatus of claim 14, wherein solid lubricant coating comprises a material selected from the group consisting of gold, silver, platinum, cobalt oxide, boron nitride, boron oxide, and mixtures thereof.
 17. The apparatus of claim 1, wherein: said first component comprises a ceramic rotor having a first set of Hirth teeth, said second component comprises a metal rotor having a second set of Hirth teeth engaging said first set of Hirth teeth, said first component is axially aligned with said second component, and said interfacial layer comprises a solid lubricant coating disposed on said second set of Hirth teeth.
 18. An apparatus, comprising: a ceramic component; and a metal component rotatably coupled to said ceramic component via a Hirth serration coupling.
 19. The apparatus of claim 18, wherein: said Hirth serration coupling defines a Hirth teeth interface between said ceramic component and said metal component, and the apparatus further comprises: an interfacial layer disposed at said interface.
 20. The apparatus of claim 19, wherein said interfacial layer comprises a solid lubricant coating or a multi-layered pre-formed metal sheet.
 21. The apparatus of claim 20, wherein said solid lubricant coating comprises a noble metal layer sputter coated on said metal component.
 22. The apparatus of claim 20, wherein said multi-layered pre-formed metal sheet comprises: an inner substrate layer, a first lubricant layer disposed on a first surface of said substrate layer, a soft metal layer disposed on a second surface of said substrate layer, and a second lubricant layer disposed on said soft metal layer, wherein: said first lubricant layer lies adjacent to said metal component, and said second lubricant layer lies adjacent to said ceramic component.
 23. An apparatus, comprising: a first component comprising a ceramic rotor and having a first set of Hirth teeth; a second component comprising a metal and having a second set of Hirth teeth for engaging said first set of Hirth teeth to provide a Hirth serration coupling of said first component to said second component; and an interfacial layer disposed at said Hirth teeth interface, wherein said interfacial layer comprises a solid lubricant coating or a compliant metal layer.
 24. The apparatus of claim 23, wherein said compliant metal layer comprises a multi-layered pre-formed metal sheet including: an inner substrate layer, a first lubricant layer disposed on a first surface of said substrate layer, a soft metal layer disposed on a second surface of said substrate layer, and a second lubricant layer disposed on said soft metal layer.
 25. The apparatus of claim 23, wherein: said Hirth serration coupling defines a Hirth teeth interface between said first set of Hirth teeth and said second set of Hirth teeth, a coefficient of thermal expansion (CTE) mismatch exists between said first component and said second component, and said interfacial layer is adapted for allowing radial sliding motion of said second component relative to said first component at said Hirth teeth interface. 